The present invention relates to optical inspection means, and more particularly to an automated system for detecting inclusions in generally cylindrical blanks of material.
Although many aspects of the production of glass and similar materials have been highly automated, certain aspects of quality control procedures have remained substantially subjective. In particular, the method commonly used for detecting inclusions in glass has taken two forms. In order to detect inclusions in in-process glass material a small portion of the molten material is typically drawn off and molded into an appropriate form termed a glass "patty". The patty is then inspected by a qualified individual using optical aids such as magnifying glasses and the like. The type, number and size of inclusions are then taken to be representative of the batch of glass in accordance with usual sampling procedures. If the nature of the inclusions is such as to suggest that a batch of glass is below some predetermined standards the batch may be reinspected, reprocessed, or scrapped.
Another technique is known and frequently used for inspecting cylindrical glass blanks, particularly blanks to be drawn into elongate optical waveguides. As is understood by those skilled in the art, due to the extremely small size of optical waveguides and to the character of the signals which they are called upon to transmit very small inclusions in a blank may render it useless. At the same time, certain types of inclusions may be acceptable for use in a waveguide blank depending upon their density, i.e., their closeness to one another. In order to inspect such blanks, they are conventionally immersed in a liquid having an index of refraction substantially the same as the glass. The blanks are then visually inspected using conventional apparatus such as magnifying glasses and the like.
It will be apparent that such inspection procedures leave much to be desired. In particular it is extremely difficult for an individual to count the number of small inclusions which are close to one another, or to accurately characterize the spatial distribution of a group of inclusions. Since the inclusions lie within the volume of the glass member under inspection it is impossible to measure their position directly.
Still further, it is often important that the type of inclusion be recognized. Inclusions may generally be classified in two groups: solid inclusions, which are formed by bits of unmelted or foreign material; and void inclusions, commonly formed by bubbles of gas. Solid inclusions generally are formed by minute impurities in the starting materials which are fused to form a glass; bits of refractory material from the walls of the vessel in which the glass is prepared; or bits of platinum from the walls of conduits through which the glass stream flows. In some cases, the solid inclusions are opaque; in others, they are clear. It is then apparent that differentiating a clear inclusion from a void inclusion, or gas bubble, can present difficulties in visual inspection. Nonetheless it is increasingly important that such inclusions be counted, properly characterized, and their spatial distribution established. Still further, for the case of materials which are opaque to visible light the detection of various types of inclusions has heretofore been practically impossible to achieve on a commercial basis. It will therefore be understood that it would be highly desirable to improve the integrity of inspection procedures beyond their present levels.
It is therefore an object of the present invention to provide means for automatically inspecting a generally cylindrical blank of material for inclusions.
It is another object of the invention to provide means for automatically scanning a blank of material which is transparent to electromagnetic radiation with a beam of such radiation for detecting inclusions.
Another object is to provide a method of scanning a generally cylindrical blank of glass or the like.
Still another object is to provide a system for defining the location of individual inclusions within a cylindrical blank.
Another object is to provide a system which automatically scans a blank of material with a beam of electromagnetic radiation and determines the number of inclusions detected and their relative position.